Remove coverage from release builds
Remove coverage from release builds

This also switches to use clang globally instead of GCC which helps reduce built-in dependencies to the pre-built binary
jdgarcia/nodegit,jmurzy/nodegit,nodegit/nodegit,jdgarcia/nodegit,jdgarcia/nodegit,nodegit/nodegit,Gum-Joe/nodegit,Gum-Joe/nodegit,jmurzy/nodegit,jmurzy/nodegit,jdgarcia/nodegit,nodegit/nodegit,jdgarcia/nodegit,nodegit/nodegit,jmurzy/nodegit,Gum-Joe/nodegit,nodegit/nodegit,jmurzy/nodegit,Gum-Joe/nodegit